Heretofore, a beam scanning method of emitting a beam from a small-diameter aperture to scan a sectoral region for acquiring a broad field of view has been widely employed in ultrasonography. Examples of the method include so-called sector scan and so-called convex scan. A broader field of view is more advantageous to find a lesion. However, it is also true that a smaller aperture diameter may be more advantageous in some cases as follows. Specifically, the smaller surface area a probe has, the more advantageous it is in such cases as where an area available for the probe contact is limited in a subject to be examined. Examples of such cases include where the probe needs to be pressed against a narrow area between ribs such as in imaging a heart. However, if a surface area of a probe is reduced, the number of rasters obtained therewith is also reduced. If scan conversion is performed on data with a reduced number of rasters so as to display the data on a video display, the resultant image will be degraded. Patent Document 1 discloses a method for preventing such image degradation. In this method, a received signal is converted into a complex signal, and a real part and an imaginary part of the complex signal are individually interpolated by using sinc functions.
[Patent Document 1] JP-A 11-9603